In the production of oil and gas from wells, brine (salt water) frequently is a by-product which occurs in substantial quantities and which presents a significant disposal problem. In some wells, the amount of brine that is produced exceeds the amount of oil that is produced. Traditionally, disposal of brine has been accomplished by placing the brine in open clay or shale pits allowing the water to evaporate. However, it has been determined that leakage from such pits caused by poor construction or by over-filling presents a serious risk of contaminating local ground water supplies. Consequently, many oil and gas producing states have enacted legislation which prohibits utilizing open pits for brine storage and disposal.
As one alternative to disposing of the brine by open pit evaporation, oil and gas producers have turned to utilizing injection wells, wherein brine is injected under high pressure into suitable formations. However, this method of brine disposal has a number of disadvantages. One disadvantage is that the brine must be transported from the site where it is produced to the site of the injection well. Transportation of brine may be difficult because some well sites are located in rugged terrain where improved roadways are unavailable. Examples of such well sites may be found in sites located in the Clinton Sand Formation of the Appalachian Basin. During periods of inclement weather, many of these well sites may be inacessible to brine transportation vehicles. A further problem associated with transporting brine is that well sites may be scattered over a wide geographic area.
Utilizing injection wells for disposal of oil well brine is expensive. Currently, the cost to an oil producer for the transportation and deep well injection of brine is between $1.40 and $2.00 per barrel. Additionally, injection wells are considered to be hazardous waste sites which require governmental approval and permits. Obtaining these permits can be a time consuming and expensive process. Injection wells also are enormously expensive to drill and complete, currently costing approximately $400,000.00 to $500,000.00. Furthermore, there is no way to determine if a target formation will accept brine until after a well has been completed. In addition to the costs involved in drilling injection wells and utilizing them for disposal of brine, there is concern that in some areas of the country, the injected brines may not remain in the target formation but may, over a period of time, migrate vertically into other formations and eventually reach fresh water reservoirs. A further disadvantage to utilizing injection wells for the disposal of brine is that none of the useful salts or the valuable trace elements and heavy metals in the brine are recovered. Salts such as sodium and calcium chloride are useful for melting ice and snow on roads. Other constituents such as potassium, magnesium, bromine, iodine, strontium, lithium, iron, aluminum, zinc, molybdenum, niobium, etc. have significant commercial value.
Many states have enacted legislation which mandates an environmentally safe method of brine disposal and storage and which imposes substantial fines for spillage of brine. At the present time there are not enough injection wells or brine haulers to handle the demand for injection well disposal. Therefore, oil producers who depend upon this method of disposal may be forced to stop pumping (shut-in) the well when adequate transportation or storage facilities for brine are not available. For some wells the cost of brine disposal is insignificant compared to the amount of revenue lost by having the well shut-in.
Another currently used alternative to disposing of brine by open pit evaporation is annular disposal. In annular disposal, brine is returned to a formation that will accept it by having it flow downwardly between the production tubing and the casing pipe of the well that produced it. To ensure that the brine flows into the receiving formation, a plug is set between the casing and the production tubing and the casing pipe is perforated at the depth of the receiving formation. Of course, this method of disposal is limited to those wells that pass through formations that are suitable for accepting brine and that can accept all the brine that is produced from the well.
Relatively small quantities of brine have been used to spray roads to control ice and snow in the winter and to control dust in the summer. However, because of the adverse impact brine may have on the environment around the roads, legislation has been enacted in many areas which prohibits such spraying. This method of disposal also requires transportation of the brine which is expensive and which may be unreliable.
It is desirable to provide means for disposing of oil well brine which does not affect the environment adversely, which does not require utilization of an apparatus that requires a large capital investment such as an injection well, which does not require transportation of the brine, which is relatively inexpensive and maintenance free, and which allows recovery of the valuable constituents contained in the brine.